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Nov. 8, 2010 (Atlanta) -- Despite fears to the contrary, common adult vaccinations are not associated with an increased risk of developing rheumatoid arthritis, a large study suggests.

Swedish researchers studied 1,998 people with RA and 2,252 people who did not have the disorder.

A total of 31% of people with RA reported they had been vaccinated within the five years prior to disease onset, says Camilla Bengtsson, PhD, an epidemiologist at the Institute of Environmental Medicine of the Karolinska Institute in Stockholm.

The same portion of people without RA -- 31% -- said they had been vaccinated, she says.

To avoid bias, the groups were matched based on age, gender, and place of residence.

"Vaccines did not increase the risk of rheumatoid arthritis," Bengtsson tells WebMD.

Additionally, there was no association between any specific vaccine -- influenza, tetanus, diphtheria, tick-borne encephalitis, hepatitis, polio, or pneumococcus -- and the risk of developing RA, she says.

The findings were presented here at the American College of Rheumatology 2010 Annual Scientific Meeting.

Concerns That Vaccines May Drive Inflammation

Bengtsson says that while there have been no well-designed studies showing a link between adult vaccines and RA, some research in rodents suggests the adjuvants used in many vaccines may affect the development of the disorder. Adjuvants are compounds added to vaccines that stimulate the immune response.

There is also a theoretical concern as both RA and vaccines affect the immune system, says Alan K. Matsumoto, MD, of Arthritis and Rheumatism Associates in Washington, D.C. He moderated a news briefing to discuss the findings.

In rheumatoid arthritis, the immune system is inappropriately turned on, causing inflammation, predominantly in the joints. This, in turn, can cause pain and lead to permanent joint damage.

"There have been concerns that vaccines by their very nature stimulate the immune system. So theoretically that could drive inflammation and increase the risk of rheumatoid arthritis," Matsumoto tells WebMD.

"The current study is very powerful due its large size. For those who had concerns, it should be reassuring," he says.

This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.